Along the LEP sites CERN is discharging water of differing quality and varying amounts into the local rivers. This wastewater is not only process water from different cooling circuits but also water that infiltrates into the LEP tunnel. The quality of the discharged wastewater has to conform to the local environmental legislation of our Host States and therefore has to be monitored constantly. The most difficult aspect regarding the wastewater concerns LEP Point 8 owing to an infiltration of crude oil (petroleum), which is naturally contained in the soil along octant 7-8 of the LEP tunnel. This paper will give a short summary of the modifications made to the oil/water separation unit at LEP Point 8. The aim was to obtain a satisfactory oil/water separation and to install a monitoring system for a permanent measurement of the amount of hydrocarbons in the wastewater

Rühl, I

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EUROPEAN LABORATORY FOR PARTICLE PHYSICSLABORATOIRE EUROPEEN POUR LA PHYSIQUE DES PARTICULESPresented at the 2nd ST WorkshopChamonix, France, February 2 - 5, 1999CERN-ST-99-017February, 1999MONITORING THE WASTEWATER OF LEPI. RuehlAbstractAlong the LEP sites CERN is discharging water of differing quality and varying amounts intothe local rivers. This wastewater is not only process water from different cooling circuits butalso water that infiltrates into the LEP tunnel. The quality of the discharged wastewater has toconform to the local environmental legislation of our Host States and therefore has to bemonitored constantly. The most difficult aspect regarding the wastewater concerns LEP Point8 owing to an infiltration of crude oil (petroleum), which is naturally contained in the soilalong octant 7–8 of the LEP tunnel. This paper will give a short summary of themodifications made to the oil/water separation unit at LEP Point 8. The aim was to obtain asatisfactory oil/water separation and to install a monitoring system for a permanentmeasurement of the amount of hydrocarbons in the wastewater.21 INTRODUCTIONThe main part of the Large Electron Positron collider (LEP) and the related installationsare water-cooled. There are different water circuits for the varying demand of users in termsof water temperature, water quality, pressure and flow rate. The sewage, which has to bedischarged from LEP, comes from the open raw-water circuit, the water treatment, tunnelinfiltration, water leaks and condensation.2 SEWAGE CIRCUITSFor the discharge of the above sewage the following circuits have been installed at LEP.2.1 Discharged-water circuit (Réseau eau rejet)The consumption and discharge of raw water depends mainly on the energy requirementof LEP and the time of year; there is however a permanent discharge of raw water all yearround. This is mainly because of• automatically flushed filter units for the primary water circuit,• measurement of the conductivity in an open analysing circuit,• evaporation losses and associated deconcentration of the primary water which has tobe compensated,• minimum flow rate of the raw-water supply pumps for the primary water circuit.The discharged water arrives at LEP Point 1 from where the water is discharged into theriver ‘Nant d’Avril’. A permanent monitoring of the radiation, the pH and the temperature isdone. 2.2 Basin for neutralization (Fosse de neutralisation) The demineralized water for the LEP cooling circuits is produced in building 378 at theMeyrin site and is afterwards distributed from there to all LEP points. The equipment toproduce demineralized water and the demineralizer, which are installed in each demineralizedwater circuit to ensure the quality of the water, have to be recycled periodically. This is alsodone in building 378. Demineralized water is collected here in a basin for neutralization,where the pH value is continuously monitored. Before the basin is discharged, the water willbe treated to set the pH value between 6.5 and 8.5. The basin has a volume of about 60 m3 andis discharged about once a month directly to the purification station at Peney, Switzerland.  2.3 Used-water circuit (Réseau eau usée) The used water from the sanitary stations is discharged like the normal domesticsewage. Raw water is added to the collecting pit for used water to facilitate the pumping ofthe viscous used water from the underground area to the surface.  2.4 Clear-water circuit (Réseau eau claire) The designation ‘CLEAR WATER’ does not relate to the quality of the water. Theclear-water circuit is in fact the drainage-water system for the LEP tunnel and it collects allthe water from the LEP tunnel.3• About 64 m3/h spills into the drainage system due to the open cooling circuits of thesixteen ‘alveoles’ along the LEP tunnel.• The infiltrated water of the LEP tunnel has also to be evacuated by the drainagesystem. The exact amount of infiltration cannot be determined. In general, weestimate an infiltration of up to 4 m3 per hour. This value is not at all applicable forLEP octant 2–3. There is an infiltration of approximately 70 m3 per hour. Toevacuate this huge amount of water, a special drainage system to LEP Point 32 hasbeen installed.• The water, which is to be evacuated owing to modifications or maintenance of oneof the LEP underground water circuits, is also collected via the drainage system.This could be raw water, primary water, demineralized water or mixed water.• Small amounts of leakage and condensation water also spill into the drainagesystems.This water is pumped from each underground cavern of the LEP tunnel to the surfaceand then discharged into the local rivers. TIS-TE is taking monthly samples from the riversfor analysing the pH, temperature, conductivity and concentration of dissolved oxygen. TIS-RP is taking once-a-year samples of water, sediments and plants at the river inlets to measurethe radioactivity.3 LOCAL ENVIRONMENTAL LEGISLATION OF OUR HOST STATESAlthough most of the water of LEP is discharged into French rivers, CERN adheres tothe much tighter Swiss law [Ordonnance sur le déversement des eaux usées (RO 1975 2403)].The slight differences in the French law [Les normes de rejet (Arrêté du premier mars 1993)]are also fully applied by CERN whenever this law indicates stricter monitoring than the Swisslaw (Table 1). The Swiss law defines limit values for more than 50 parameters and,obviously, it is not possible to survey them all continuously. Hence most of the processes aremonitored according to their specific use by taking into account the major risks. In most casesa permanent measurement of the pH and the temperature is adequate. Owing to the specificuse at CERN the radiation of the discharged water has also to be monitored.Table 1Differences in Swiss and French law of some limit valuesParameter Swiss law French lawpH 6.5–8.5 5.5–9.5Temperature 25°C [30°C] 30°CConcentration of dissolved oxygen 6 mg O2/lConcentration of hydrocarbons 10 mg/l 15 mg/lRadiation44 LEP POINT 8The monitoring of the discharged clear water of LEP Point 8 is different from all theother LEP points. A more detailed description of the situation at LEP Point 8 is thereforenecessary.4.1 Infiltration of water and petroleumIn the two LEP octants 6–7 and 7–8 there is also an infiltration of petroleum (naturalcrude oil), which is naturally contained in the soil. Naturally occurring petroleum is complexand variable in chemical composition. Its colour ranges from light greenish brown to black. Itmay be fluid or so viscous as to be nearly solid.4.2 Consistency of the oilThe analysis was done by SHELL in 1988. The sample consisted of a mixture of• 10% volume of sediments (sand, etc.),• 40% volume of water,• 50% volume of hydrocarbons. The mixture indicated the following values:• density of 0.972 kg/ dm3,• kinematic viscosity of 568 cSt (centistokes) by 50ºC [1cSt = 10-6 m2/s = 1 mm2/s],• 0.27% weight of sulphur. The phase of hydrocarbons showed• 70% volume distilled by a temperature lower than 370ºC, and can be seen thereforeas light oil;• 30% volume has to be considered as heavy oil. This analysis shows that the raw petroleum is to be considered as very heavy (bitumen)with a very high inflammation point.  4.3 Emulsion An emulsion is an intimate mixture of two liquid phases, such as oil and water, in whichthe liquids are mutually insoluble and where either phase may be dispersed in the other. Anoily waste emulsion, in which oil is dispersed in the water phase, may contain any of varioustypes of oil in a wide range of concentrations. Violent mixing and shearing of oily wastewaterin transfer pumps disperses these minute oil droplets throughout the water.  4.4 Treatment methods Oil separation and removal can be divided into two processes: gravity separation offree, nonemulsified oil and chemical treatment and separation of emulsified oil. Oily waste istypically a combination of free, nonemulsified oil, stable emulsified oil and insoluble solids.Settable-free oils and insoluble solids are physically removed from wastewater by gravityseparation. Such gravity separators cannot remove soluble impurities nor break emulsions.5Gravity separators depend on density differences to provide the buoyant force that causes thedroplets of free oil to rise to the surface. Theoretically, oil droplets rise linearly as predictedby ‘Stokes’11 law; in practice, turbulence and short-circuiting usually disturb the separationpattern. vg =d 2 * (δ w − δ o )18η* g (1) νg - liquid droplet rise velocity [m/s] d - particle/droplet diameter [m] δw - water density [kg/m3] δo - oil density [kg/m3] η - dynamic viscosity [kg/(m*s)] g - gravity [9.81 m/s2]  The above expression shows that the sedimentation of a particle (droplet) is determinedby the physical characteristics of the particle/droplet in the continuous phase. The mainfactors that affect the design of an oil-water separator are accordingly• Flow rate (average, maximum, and minimum).• Specific gravity of the oil.• Viscosity of oil.• Operating temperature,• Fluid characteristics: % of free oil, % of soluble oil, diameter of oil globules, andextent of mechanical emulsion.• Identification of other contaminants present in feed stream. 4.5 Modifications made to the water–oil separation unit at LEP Point 8 The crude oil comes mainly along the lowest point and the two alveoles RE 78 and RE82. To diminish the amount of clear water to treat at the water-oil separation unit, the twocooling circuits for the alveoles RE 78 and RE 82 have been modified. The primary-watercircuit is now a closed demineralized-water circuit. The main modifications have been madeto the decantation basin.• Cleaning and discharge of more than 20 m3 of oily sedimentation from thedecantation basin.• Increasing the capacity of the basin, by building up each restraining wall by 50 cm,to handle higher flow rates by maintaining the water quality.• Installation of a new filter system (mousse de polyuréthane floquée) with a ten timeslarger filter surface.• Installation of an oil skimmer that can be moved from one chamber of thedecantation basin to the other to skim the oil from the water surface. This oilskimmer reduces the cleaning of the decantation basin almost to zero.• Seven new overflow holes (siphons), adjustable in height, have been installed whichcan also be used to drain the surface water.1 Stokes, Sir George Gabriel (1819-1903); British physicist and mathematician noted for his studies of thebehaviour of viscous fluids.6• The oil, which is collected via an oil skimmer and via the siphons into the collectingchannel, is discharged by ORTEC for incineration.• For a constant measurement of the quantity of hydrocarbons in the sewage leavingthe decantation basin, a photometer is installed in the SUX 8 building. Themeasurement is a continuous analysis of the fluorescence of the water and acontinuous comparison with a chemical source (quinine sulphate) of fluorescence,which corresponds to 100% of crude oil. The photometer calibrates itselfcontinuously. The results of the analysis are transferred to the LabVIEW controlsystem. The ‘Département des travaux publics de Genève’ is also taking samplesonce a month. The latest results have shown that their analyses are in agreementwith the measurements of the photometer.• A valve of DN 400 has been installed on the outlet of the decantation basin, whichwill close if the amount of hydrocarbons exceeds the allowable maximum of 10 mgof hydrocarbons per litre of water, to avoid sewage spill into the river ‘Nant duGobé’.• The constant monitoring of the water quality allowed us to create different alarmlevels.Today the water–oil-separation unit consists of two oil separators and a decantationbasin, equipped with an oil skimmer, seven overflow holes (siphons), three vertical and onehorizontal filter that allow a satisfactory oil/water separation. The entire water–oil-separationunit is a static process based on separation per gravity, which means that changes in the flowrate will effect the quality of the separation directly.4 CONCLUSIONThroughout the years of LEP experiments there hasn’t been any law-breaking incidentdue to the discharge of LEP wastewater. With regard to LHC, the wastewater which has to bedischarged will be far less than today because almost all cooling will be done in closedcircuits. Nevertheless the monitoring of the discharged clear water will be extended becauseof the higher expected radiation for the LHC.Concerning LEP Point 8, the infiltration of crude oil will continue indefinitely. Hencethe monitoring of the sewage and the installations has to be maintained properly to guaranteea satisfactory oil/water separation.References[1] Frank N. Kemmer, The NALCO water handbook (McGraw-Hill, London, 1988).[2] Robert H. Perry, Don W. Green, James O. Maloney, Perry’s chemical engineers’handbook (McGraw-Hill, London, 1984).[3] Alfa Laval, Theory of separation (Sandström & Söner, Tumba, 1995).[4] W. Beitz, K.-H. Küttner, Dubbel - Taschenbuch für den Maschinenbau (Springer,Berlin, 1990).[5] C. Bertoux, R. Magnier, C.W. Nuttall, M. Renou, P. Vojtyla, Monitoring of non-radiation environmental parameters at CERN – Annual report 1997 (TIS-TE, CERNGeneva, 1998).

Monitoring the waste water of LEP

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